Dr. T. Berry Brazelton, America’s most celebrated baby doctor since Benjamin Spock and the pediatrician who revolutionized our understanding of how children develop psychologically, died on Tuesday at his home in Barnstable, Mass., on Cape Cod. He was 99.

His daughter Christina Brazelton confirmed the death.

Before Dr. Brazelton began practicing medicine in the early 1950s, the conventional wisdom about babies and child rearing was unsparingly authoritarian. It was believed that infants could not feel pain. Parents were instructed to set strict schedules, demand obedience and refrain from kissing or cuddling. Babies were to be fed every four hours, by the clock, preferably from a bottle. When children were hospitalized, parents were allowed few if any visiting hours.

Dr. Brazelton rejected such beliefs and practices as being senseless, if not barbaric.

“He put the baby at the center of the universe,” Dr. Barry Lester, a pediatrician and director of the Center for the Study of Children at Risk at Brown University, said in an interview for this obituary in 2009. “We take for granted all the changes he helped bring about. He more than anyone is responsible for the return to natural childbirth, breast feeding and the ability of parents to stay with a hospitalized child.”

Nevertheless, Dr. Brazelton’s work never entered mainstream pediatrics and is not taught in most medical curriculums.

But the public loved the charismatic Dr. Brazelton. He wrote nearly 40 books and a column in Family Circle magazine, and he was the host of an Emmy Award-winning show, “What Every Baby Knows,” which ran for 12 years on the Lifetime cable channel.

He also worked with Congress to pass parental leave legislation and other parent-friendly measures.

Dr. Brazelton had a remarkable talent for handling infants and eliciting behaviors that no one before him had noticed. For example, he would hold a day-old infant in front of his face, lock eyes and move his head side to side. The baby followed. He developed strategies for how to get a baby to be quiet, to fall asleep, to come back to an alert state.

The more he worked with newborns, the more he realized that they are complex, responsive and competent at birth, using behavior as their language. The movement of an arm or leg told him if they were feeling disorganized, stressed or good. Little hiccups might mean their nervous system was unstable.

He realized that babies have the ability to control their internal state and to become engaged, or disengaged, according to what is happening in the world around them.

Dr. Brazelton was one of the first researchers to use videotape to observe the dynamic interplay between mothers and infants. By freezing frames and replaying them hundreds of times, he was able to capture the subtleties of face-to-face interactions.

The video camera became a tool for observing behavior, showing how mothers and infants cycle through rhythmic interactions lasting 15 to 20 seconds. The infants lead, the mothers follow. When a mother stops responding by putting on a deadpan face, her baby quickly becomes upset.

The notion of mother-infant bonding, now gospel among early-childhood experts, grew out of this research, but Dr. Brazelton took it one step further — back into the clinic. He found that premature infants follow the face-to-face interactions and that the mothers lead. The babies are fragile, he said, and need extra help from their mothers.

From these observations, Dr. Brazelton wrote a book, “Infants and Mothers: Differences in Development” (1969), which argued for the first time that newborns arrive in this world with a biologically based temperament. Moreover, he wrote, this intrinsic personality affects how parents interact with their infants: The infant’s temperamental repertoire drives the parenting style.

Dr. Brazelton in 2006. “He put the baby at the center of the universe,” said Dr. Barry Lester, a fellow pediatrician.CreditM. Spencer Green/Associated Press

Thus a hypersensitive baby might continually turn away from his mother’s gaze, causing her to feel rejected. But if the mother understands her infant’s sensitivity, she will not overwhelm him. Easygoing babies, on the other hand, are able to handle much more stimulation. The notion of human resilience — defined as successful adaptation in the midst of challenging or threatening circumstances — grew out of this research.

In 1973, Dr. Brazelton published the Neonatal Behavioral Assessment Scale, a method to elicit all the behaviors a newborn might have in a 24-hour period, including crying and self-soothing, within 20 minutes. The scale is intended to note an infant’s best performance on 28 items involving how well they manage their sensory awareness. Some are bothered by bright lights and loud sounds, others not. Some can be soothed by swaddling, others not. Each infant has a different style for self-organizing.

The N-Bas, as it became known, was criticized by many pediatricians, because, they noted, an infant’s score on one day did not necessarily correlate with its score on another day. Scores, they said, should be stable, like I.Q. But Dr. Brazelton was shocked by that view.

“Why would I want or expect a baby’s score to stay the same from day to day?” he said. “If a baby does not change, then I worry.”

In working with more than 25,000 infants and children over his career, Dr. Brazelton had another important insight: Development does not occur on a linear path, with each skill building on earlier ones. Rather, it unfolds in a series of major reorganizations in which children temporarily regress before mastering a new developmental milestone.

Just before a surge of rapid growth in any line of development, the child’s behavior seems to fall apart. Parents lose their own balance and become alarmed.

“People now take this for granted,” said Dr. Joshua Sparrow, an associate professor of psychiatry at Harvard Medical School who collaborated with Dr. Brazelton. “But Berry started it before developmental neuroscientists came along to show that he was right.”

In 1993, the Brazelton Institute was founded at Boston Children’s Hospital as a way to spread Dr. Brazelton’s findings on babies and children. In 1998, Dr. Brazelton and his colleagues began Touch Points, a clinical program offered at 100 sites around the United States and abroad. (Dr. Sparrow is the director of the program at the Boston hospital.)

Touch Point Centers reach out to early-childhood educators and to health-care and social-service providers with this message: Before a child makes a new developmental leap, he falls apart. He is going back to gather his strength to take the next leap. If you can help parents understand what is coming, they can anticipate what will happen in normal development.

Dr. Brazelton believed that parents visit pediatricians not primarily to treat diseases. Rather, they come with questions about healthy development involving sleep, feeding, toilet training, tantrums and other behaviors. His advice to parents: Learn to read your baby’s language. Look at your baby. He will tell you what he needs. Trust your gut reaction. Parents, he said, need as much support as their babies do.

Dr. Brazelton went public with this and other messages in a big way. He was a popularizer, in the tradition of the astronomer Carl Sagan, but his critics said he was too visible, and that he was overly artificial and sunny.

Thomas Berry Brazelton Jr. was born on May 10, 1918, in Waco, Tex., to the former Pauline Battle and Thomas Berry Brazelton. He showed an early interest in caring for children,

“At every family event,’’ he recalled in his 2013 memoir, “Learning to Listen: A Life Caring for Children,’’ “I was put in charge of all nine first cousins while aunts and uncles and grandparents prepared for the big dinner.’’

To please his grandmother, he added: “I became adept at handling many small children at once. I could keep them amused and safe and keep them from crying for up to two hours at a time. A miraculous feat, I realize today!”

By the sixth grade, he had decided on a career in pediatrics — or maybe the stage. He loved acting and singing.

At Princeton University, from which he graduated in 1940, he tried out for and was offered a role in a Broadway play with Ethel Merman. His father insisted that he go to medical school instead. He did, graduating from Columbia University College of Physicians and Surgeons in 1943.

After an internship at Roosevelt Hospital in New York and a year in the Naval Reserve, Dr. Brazelton began a medical residency in 1945 at Massachusetts General Hospital in Boston. He took his pediatric training at Boston Children’s Hospital in 1947 and went on to study child psychiatry at Massachusetts General and the James Jackson Putnam Children’s Center.

Dr. Brazelton began a private practice in pediatrics in Cambridge, Mass., in 1950 and was appointed instructor at Harvard Medical School. In 1972, he established the Child Development Unit, a pediatric training and research center at Children’s Hospital.

In 1988, he was named clinical professor of pediatrics emeritus at Harvard Medical School and professor of psychiatry and human development at Brown University. Harvard Medical School established the T. Berry Brazelton Chair in Pediatrics in 1995. In 2002, he received the World of Children Award for his achievements in child advocacy.

In addition to his daughter Christina, he is survived by two other daughters, Catherine and Pauline; a son, Thomas III; and five grandchildren.

His wife, the former Christina Lowell, who at one time ran an art gallery and served on the boards of several nonprofits, died at 94 at their Barnstable home in 2015. Her father, Alfred Putnam Lowell, was a Boston lawyer and a cousin of the poet Robert Lowell. She was also a descendant of John Lowell, a federal judge appointed by President George Washington.

Dr. Brazelton met her at a dinner party at Alfred Lowell’s house in 1949. Smitten, he later asked if he could visit her in New York City, where she worked for the Putnam publishing company.

“To bolster my chances,” he wrote in his memoir, “I took along a copy of an avant-garde poetry magazine with her cousin Robert Lowell’s work in it.”

“ ‘Do you read this?’, she asked.

“ ‘Of course,’ I lied.”

They were married that year.

When it came to their own children, Mrs. Brazelton did not always subscribe to husband’s child-rearing theories, The Boston Globe reported.

“She’d say, ‘I don’t want to hear any advice from you,’ ” The Globe quoted Dr. Brazelton as saying. “We went back and forth all the time. We argued for 66 years, and I always let her win. It kept everything alive.”